(T) Punto Temperature Gauge: A tad erratic .. Any ideas?

Hi there

I have a Punto 1.2 ELX. It's about 5 years old and done about 30,000 miles - been serviced regulary - last time was May this year.

I have noticed for a while now that the temperature gauge, when driving, can be a little erratic. What I mean by this, is that it will never ever go above half way (which has always been the 'max' on the gauge that it has ever reached) but it will sometimes, when driving along (mainly at high speeds) drop very quickly from the half way mark down to only say a quater on the gauge, or even a little below this - then it will go straight back to the half way mark again.

Occasionally it will also slowly move down from the half way mark and then hover back to it - as I say - it never ever goes above half way. Today, for example, when driving home, it took its time warming up to the half way mark (as is perfectly normal for the cold engine of course)- but a couple of times, whilst driving at speed it dropped dramatically and quickly - then very quickly back to the half way mark - I am sure the oil light came on when it dropped quickly - only for a brief second though. I have checked the oil and water and all is ok.

Does anyone have any ideas what could be happening here please? Could it be the thermostat sticking or something? Is it likely to be doing the car any harm? I know obviously not to drive it etc if the gauge was shooting upwards, but as I say, it never moves higher than the half way mark - most of the time this is where it stays too - but - the occassional quick drop and then back again on the gauge worries me a little....

Any help or opinions really appreciated

Thanks

Paul

The first bit is easy to answer.

You never want the gauge to go above the halfway mark as this is where it should be (i.e. at 45 degrees). Needle at the bottom of the gauge means the engine is stone cold (which you will have guessed), needle at top (i.e. standing vertically) means the engine is overheating and it is all going a bit pete-tong... For short periods of time (like in traffic on a hot, hot day) the needle may creep above the 45 degree mark slightly, but not by much.

As for the dropping needle, from your description this seems to correspond with the coolant temperature dropping when you change from more more challanging conditions to open-road driving. As you have guessed, this is likely to be the thermostat which needs replacing